One type of semiconductor devices is a high electron mobility transistor (HEMT) including a semiconductor stacked structure including an electron transit layer and an electron supply layer.
In recent years, efforts to develop GaN-HEMTs with a HEMT structure, have been intensified, which employs a hetero junction between AlGaN and GaN, i.e., GaN-based compound semiconductors, and includes a GaN layer as an electron transit layer and an AlGaN layer as an electron supply layer.
GaN is a material which has a band gap of about 3.4 eV, higher than the band gaps of Si (about 1.1 eV) and GaAs (about 1.4 eV), and has a higher breakdown field strength. GaN is also a material exhibiting a higher saturation electron velocity. Thus, GaN is quite promising as a material for a semiconductor device for a power source, enabling higher voltage operations and providing higher outputs. GaN-HEMTs are also promising for high-efficiency switching elements used for power supply apparatus provided in electronic apparatuses, and power devices with higher withstanding voltage used in electric vehicles.